Patent GB-1328185-A (GB)
Title: Method of joining electrically conducting bodies
IPC: H01L21/60
Filed: 1972-02-02
Abstract: 1328185 Soldering I N LARIONOV and J P CHERNETSKY 2 Feb 1972 4811/72 Heading B3R [Also in Division H1] A method of joining electrically conducting bodies e.g. semi-conductor crystals or metal for semi-conductor and electron-tube devices, comprises placing the bodies in juxtaposition so that a capillary gap exists therebetween, introducing molten low-melting material into the gap between the bodies thereby dissolving surface layers of the bodies, and passing a direct electric current through the bodies and molten material in a direction to cause the molten material to move through the gap and emerge therefrom, recrystallization of the dissolved material occurring in the gap to join the bodies together. The thickness of the interconnecting layer is dependent upon the temperature at which the process is carried out and upon the intensity of direct current applied. Where the two bodies 1, 2 are polycrystalline the interlayer 10 is polycrystalline but where the two bodies are single crystalline two single crystal layers 11, 12, (Fig. 2b) with a bicrystalline boundary layer 13 are formed. The interlayer is mainly recrystallized material from the bodies 1, 2 but carries a small proportion of the low melting material. A P-N junction may be formed between semi-conductor bodies. Reference is made to joining bodies of germanium, silicon, silicon carbide, gallium arsenide using low melting materials such as indium, gallium, tin and eutectics such as aluminium-silicon, aluminium-germanium and silicon-gold. In an arrangement for carrying out the method plate 1 is laid, after suitable surface preparation, on a plate 2 in a heating chamber adapted to be heated by electric heater 9. Low melting material in the form of a ball 3 is placed on the upper surface of plate 2. Electric contacts 4, 4<SP>1</SP> supplied by leads 5, 5<SP>1</SP> provide for the supply of direct electric current to the plates 1, 2. Contacts 4, 4<SP>1</SP> include coiled springs 6 of high melting material arranged with quartz insulating pieces 8 to ensure adequate current distribution. Heating is carried out in vacuum or under protective gas and the low melting material 3 on melting is drawn into the gap between the plates 1, 2 by capillary action. Current is then applied to cause movement of the molten material between and out from the plates to the negative terminal 4. -In an alternative arrangement (Fig. 3, not shown) a flat annular washer is joined to a flat disc the low melting material being in the form of a flat annular ring placed inside the washer on the surface of the disc. Examples are given as follows: (1) the surfaces of two rectangular plates of germanium of specific resistance 1 ohm.cm. and 0À001 ohm.cm. are prepared by grinding, polishing and chemical washing and the plates then joined in an arrangement according to Fig. 1 at 600 C. under hydrogen using indium as the low melting material; (2) a disc (14) (Fig. 3) of germanium is joined to a washer (15) of germanium alloyed with arsenic, using a low-melting material tin with 0À5% arsenic; (3) rectangular plates of silicon are joined according to Fig. 1 using silumin as low-melting material. The process is carried out under vacuum. A P-N junction is formed; (4) plates of molybdenum and silicon are joined using silumin as low melting material: (5) plates of gallium arsenide and germanium are joined using gallium as low-melting material; (6) plates of indium antimonide and germanium are joined using indium as the low melting material.